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Member postings for Turbine Guy

Here is a list of all the postings Turbine Guy has made in our forums. Click on a thread name to jump to the thread.

Thread: Testing Models
18/01/2019 21:34:12

I purchased a Chiltern Vertical Single Marine Engine. This engine has a 14mm bore, 18mm stroke, a piston valve, and Teflon piston rings. I ran my Chiltern engine for a short time and very quickly it was able to run on 5 psig (0.34 bar) air pressure. I checked the leakage holding the valve in various positions with maximum pressure. When the valve was in the position that both ports were closed there was very little leakage after the engine had been run for a few minutes and not reoiled. After I oiled the engine the leakage completely stopped in this position. This was with a pressure of 24 psig (1.63 bar), the maximum I plan to use. When I moved the valve to a position that the ports were open, the leakage started but did not seem excessive. The leakage was about the same in all positions of the valve accept at each end of its travel where it increased quite a bit. These positions are where the distance from the edge of the port to the edges of the inlet and outlet are shortest. Apparently, the valve clearance is tight enough that oil can seal it in most positions. Even after running a while the valve leakage only increased a little. The piston rings have some leakage but it doesn't appear to be excessive. The minimum pressure the engine would continue to run stayed at about 5 psig (0.34 bar). Each time I shut the compressor off when the engine was running, the speed increased before slowing down and stopping. I'm still trying to figure out what causes this. I'll add a photo of this engine in the next post.

Thread: For discussing the merits of alternative 3D CAD programs.
16/01/2019 15:22:04

Ian,

I've never paid anything. You have to pay for the full version, but if you don't mind making your models public, the free version works fine. When my friend suggested using Onshape, I went to their website and created an account. I don't remember all the details, but it wasn't difficult.

Thread: Model Turbines
16/01/2019 15:01:26

Hi all,

Thanks for your responses. Based on my modest experience with building steam engines. My simple turbine is much easier to make than a steam engine. The more efficient Terry turbine design is still much less difficult to make. My only concern with my Terry turbine design is the 0.005" minimum thickness of the blades. If the cutter can mill out the opening without bending the blades there shouldn't be any problem making the rotor. The 3/32" diameter, .015" wide, keyseat cutter is very expensive but available. My Terry turbine rotor design is a scaled down version of the Terry turbine rotor with the best performance in Dr. Balje's study of high energy level low power output turbines. I used Dr. Balje's guidelines to make a 12" diameter 8 HP steam turbine that was tested in a lab and had almost the exact performance he predicted.

Tim is taking on a much bigger project with potentially much better results. The velocity compounded impulse turbine is ideal for running at lower speeds. I hope he shares with us pictures of the turbine parts as he finishes them.

14/01/2019 21:24:45

I started this thread to create a place where we could share information about model turbines. To get the ball rolling, I'll share the information I have on my model steam turbine and a more advanced design I may build. The photos of the turbine assembled and the major parts are in my album. The drawings for these turbines are also shown in the gallery. I call my existing turbine a tangential turbine since I have not found a common name given for the open pocket tangential flow turbines. The more advanced design is for a Terry turbine rotor that can replace the tangential turbine rotor and use all the remaining parts. This is a very small turbine with a 7/8" rotor that has been run with a very small boiler and a small airbrush compressor. The testing of this turbine is given in my thread for testing model engines. I hope this information can be useful to someone looking for a very easy turbine to build.img_0182.jpg

Thread: For discussing the merits of alternative 3D CAD programs.
14/01/2019 18:14:56

After reading through the previous posts in this thread, I thought I would add a little to the comments of Rod Ashton 14/11/2018 and Muzzler 15/11/2018 concerning Onshape. Onshape was recommended to me by a friend for a CAD system after I retired. While working, I used SolidWorks but could not afford the cost for personal use. When I tried Onshape it took me almost no time to start making solid models. The assemblies have the parts connected with the same degree of freedom as the actual engine. On a engine model I can click and drag the flywheel (or any part) and move it the same way it would move in the actual engine. All the parts connected to the part being moved will also move the same as they would in an actual engine. This is a tremendous help for checking clearances, determining valve settings, and seeing the effects of adjustments. Onshape allows me to make any model almost as easily as SolidWorks without any cost.. The only downside is the files are public, so anyone on Onshape has access to them. This doesn't bother me since I feel if anyone whats to share my files for their own use they are welcome to use them. They can copy parts, assemblies (including all parts) and do what ever they want with the copies. They can't change the originals since they can only be changed by the creator.

Thread: Testing Models
08/01/2019 22:46:12

I found an error in my calculations for the power output of my ST engine. The corrected total power loss due to friction is approximately 2.55 watts and the resulting calculated power output is 0.7 watts. This leaves a little more loss unaccounted for, but the result is about the same. In my calculations I used the friction given by Parker for a floating 0-ring even though I ran the last tests with the tight packing. I needed some method to calculate the friction when the seal gets pressed against the cylinder bore by pressure. Since I got almost identical performance with the 0-ring and the tight packing in earlier tests I thought this method was valid for either. The only unknown in the rest of the calculations is the friction coefficient. This varies with the materials used, the finish, and whether dry or lubricated. The value of 0.3 I used for the friction coefficient is what I have seen used before for estimating the friction. Because of these unknowns the calculations are only indicative of the approximate size of these losses.

07/01/2019 19:19:46

I’ve run the ST engine with the tight packing and the increased cylinder shaft size off and on for about a half an hour and the maximum speed is up to about 900 rpm now. Since my airbrush compressor is able to maintain a pressure of 20 psig at the maximum speed the engine is running and the power output is very low, I tried to estimate the power losses. I looked at the friction power loss at each of the motion points and estimated the total power loss due to friction is approximately 2.68 watts. I use a friction coefficient of 0.3 for the analysis. I estimated the pressure drop in the inlet port to be 1 psi. I estimated the pressure drop in the exhaust port to be 4 psi. With these pressure drops, the existing clearance volumes, and the cut off point of the ports I calculated the mean effective pressure. I estimated the mean effective pressure to be approximately 15 psi and the corresponding indicated power to be 3.25 watts. Subtracting the friction power loss from the indicated power gave a power output of 0.57 watts. The power required to turn the 8” propeller 900 rpm is 0.09 watts. My calculations don’t quite show where all the power was lost but confirm that the power loss due to friction and pressure drop through the ports is very high for the Stuart ST engine. The lower speed with the increased cylinder shaft size is partially explained by the engine not being fully broken in. In addition, the friction loss of this shaft goes up in direct proportion with the increase in shaft diameter. The low power output is finally starting to make sense.

06/01/2019 18:52:33

I ran my Stuart ST with the tight packing and the increased diameter cylinder pivot pin. The tilting of the cylinder face against the standard face was almost completely eliminated with the tighter clearance. With 20 psig steam pressure, the leakage was about the same with the cylinder rotated in any position and the pressure didn’t drop when the engine was at its maximum speed. I stopped, oiled, and started the engine for about a half hour. The maximum speeds for 5, 10, 15, and 20 psig were 450, 655, 765, and 851 rpm respectively. The speeds kept increasing with each run and the leakage decreased slightly after all the running. My airbrush compressor ran the full time on the first run and was turning on an off on the last run. The engine ran much smoother and quieter without the cylinder tilting back and forth on the standard. I expect the engine will reach a higher speed after it is fully bedded in since it had a maximum speed of 1,160 rpm before these changes.

06/01/2019 16:08:30

Tim,

It looks like you picked a very good turbine to base your design on. I searched on the internet for information on this turbine and found the following for a rebuilt turbine. They didn't give the temperature or the mass flow of the steam for this power. It surprised me the turbine would operate at such a low speed.

Specifications

Coppus Steam Turbine TF-9
RPM: 1250
HP: 0.75
Inlet PSIG: 75

02/01/2019 15:12:24

The preceding posts bring us up to date on all the testing I have completed so far. The descriptions of these tests were taken from Emails to Thor updating my progress. Thor helped me in my testing using his experience with the many steam engines he has made and run. These test results only show the results we were able to obtain and not some of the problems we had to overcome. You can see from these tests, it is not always easy to find what the real problems are. I was concentrating on the internal leakage of my ST steam engines and it took a long time to find that the biggest problem was the titling of the cylinder due to the loose fit of the cylinder support pin. I have machined a larger cylinder pivot pin and will drill and ream the standard of one of my ST steam engines to reduce the clearance. When I get the standard finished I will start the testing again.

02/01/2019 14:27:03

I machined the piston of by second ST steam engine for a floating o-ring. I ran the engine with the floating o-ring off and on for about a hour and a half. The results were similar to the engine with the tight packing. After all the parts bedded in, there was almost no external leakage with the cylinder in either position where all the ports were closed. When the cylinder was in either position that the inlet port was near it's maximum opening the external leakage started due to the cylinder tilting on the standard. I have no way of knowing how the external leakage compared with the engine that has the tight packing but it seemed slightly less. The top speed was about 1,200 rpm right after the engine had been oiled and then settled down to a speed of about 1,150 rpm and would hold that speed. The steady speed of 1,150 was almost the same as the maximum speed of 1,160 rpm obtained by the engine with the tight packing that had run for quite a bit longer. When I changed the cylinder assemblies on the standard used for testing, I compared the force needed to move the pistons with the ports opened and closed. The force to move the piston with the ports open was about the same. The force to move the piston with the ports closed was much higher with the floating o-ring which appeared to completely seal the piston. The engine with the tight packing took a lot more force to move the piston with the port closed than with the port open so was still sealing very good. The external leakage caused by the cylinder tilting keeps me from getting a good test of any of the seals. I was pleased with the performance of the floating o-ring since it did better than I expected with the high leakage. I need to fix the cylinder tilting problem to get good test results.

02/01/2019 14:10:07

I ran my oscillating engine with the tight packing off and on for about 2 hours. The maximum speed was 1,160 rpm. This is slightly above the 1,120 maximum speed of the last test. The bedding in and wear of the packing appears to have leveled off to a point I can consider this speed to be the maximum for my test of the tight packing. The corresponding propeller power for 1,160 rpm is 0.18 watts. I checked the external leakage with the piston in various positions and the engine stopped. With the piston in a position that all the ports were blocked the leakage was almost completely stopped and only a few oil bubbles were escaping.. When the piston was in a position where either inlet port was near it's maximum opening, the leakage increased considerably. In these positions the leakage through the mating surfaces of the standard and cylinder and the leakage by the piston and connecting rod took all the flow of the airbrush compressor at it's set pressure of 20 psig. I rotated the propeller with no air pressure and looked at the mating surfaces with a light behind them. I could not see any separation in all positions with no air pressure. I did the same thing with the air turned on and could see the surfaces separate when the inlet ports were near their fully open positions. Apparently the internal force pushing on the cylinder with air pressure is cocking the cylinder on it's support pin and causing the leakage. Stuart used a relatively loose fit on the cylinder support pin that makes it easier for this to happen. This leakage plays a big part in explaining the disappointing performance with the higher pressure.

02/01/2019 14:01:03

I attached the hose from my airbrush compressor to my boiler outlet tube to check the relief valve. The relief valve is leaking even at very low pressures and opened at approximately 20 psig, not the 25 psig that I assumed, and is the maximum steam pressure my engines have run on. I set the airbrush compressor at 20 psig to match the steam pressure and tested the engine with the tight packing. I tried different settings of the spring that pushes the cylinder against the standard. The highest speed reached was 1,010 rpm with the spring almost fully compressed. When I stopped the engine and put the cylinder in a position that both ports were closed there wasn't much air leakage with the 20 psig pressure. The maximum speed was close to the maximum speed with the air pressure set at 25 psig (1,120 rpm) so increasing the set pressure was almost offset by the increase in leakage. The actual running pressure was almost identical for the 20 psig and 30 psig set pressures. Internal leakage, pressure drop through the ports, and friction have a large effect on this small engine. I ran another test to with the pressure set at 20 psig and got a maximum speed of 1,120 again.

02/01/2019 13:45:24

I set the airbrush compressor regulator to 30 psig and started the compressor while holding the propeller in a position where the inlet port was blocked and the pressure just verily held with the airbrush compressor running almost constantly. At 30 psig pressure almost all the air could leak out of the joint between the cylinder face and the standard with the tension spring almost fully compressed. When I released the propeller, the engine initially ran at a speed of 1,060 rpm and after a fairly long run the speed reached 1,100 rpm. The air pressure was about 20 psi for the entire run. Apparently, the airbrush compressor doesn't have enough mass flow to keep up with the leakage of the engine and reach the set pressure of 30 psig . Before I tried testing the engine, the tension spring was never near fully compressed so I must have run at relatively low pressures. So far, I have never reached the performance of the very loose packing (1,500 rpm) either with steam or air. The extra friction from packing the piston as tight as I could seems to lower the performance since the tension spring does not appear to be strong enough to run at a pressure above 20 psig. I wonder if the spring tension is not enough or if the contact surfaces are not parallel. I need to cure the leakage problem before I can make any useful tests.

02/01/2019 12:52:10

Tim,

I would choose air based on my experience using both. My airbrush compressor puts out a very consistent air flow and starts with the push of a button. I'm able to use pre-lubricated ball bearings without worrying about the steam washing out the grease. I also don't have to worry about wet steam and rusting. I suggest you choose your power source and make a nozzle. You will need the maximum diameter of the nozzle for scaling the blades. You're right about using multiple nozzles and being able to isolate them individually. The supersonic nozzles are very sensitive to pressure drop and can become unstable with pressure ratios higher or lower than their design. For optimum performance the angle of the blades needs to take into account the speed difference between the stationary and moving parts. If you plan on only running at low speeds this won't be as important.

01/01/2019 20:47:00

Andrew, I assumed the steam was almost completely dry because it was almost invisible coming out of the exhaust port. After it traveled a short distance I could start to see the moisture. When using steam, I ran the engine quite a long time before starting to measure the performance so that it would be at full temperature. Using propellers for a load source definitely didn't help. One of the most important reasons I had for doing the remaining testing with a airbrush compressor was eliminating this unknown.

01/01/2019 20:25:54

I added the picture of the packing to my photo album. Sorry about the poor quality. Photos are obviously not my strong point. Before removing the piston, I tried moving it back and forth with the ports closed and only felt a slight resistance. The packing appeared very smooth and completely intact. I didn't have any new packing, so I tried repacking the piston using its existing packing and some of the packing from my second ST engine. Before removing the piston, I ran the engine with a propeller attached so that I could record the speed and power as I did with the turbine. The propeller used on the ST is a APC 8x6 and the engine ran at a speed of approximately 1,500 rpm. The propeller required 0.4 watts to turn at the speed based on the propellers performance data sheets. This was very disappointing performance, since I expected much more power. I assumed the low power was due to the poor sealing of the piston packing. I packed the piston as tight as I could and tried moving it back and forth in the cylinder with the ports blocked and could barely move the piston. The resistance was much higher with the ports open than with the loose packing. I tried a run with the tight packing but the relief valve on my boiler started leaking. I decided to to all my testing with the airbrush compressor. I'll add the results of all the testing I have completed in following posts.

01/01/2019 19:14:40

I have also ran several tests on my Stuart Turner ST oscillating cylinder steam engines. These were purchased in the 1970's and were bought as fully assembled ready to run and had not been disassembled prior to the start of the testing. I ran a very unscientific but revealing test to try to determine how effective the packing is for sealing pistons. I used my 7/16" bore and 7/16" stroke single cylinder oscillating engine for the test. I suspected that the leakage would be large enough that my small boiler would not reach full pressure with the rotation stopped and the steam port wide open. When the boiler started to make steam, I let the engine run to pass the initial condensation through. I then stopped the engine in a position that all the ports were blocked and adjusted the spring that pushes the cylinder against the standard. I had to almost fully tighten the spring to stop the leakage from the cylinder and standard interface. In this position the pressure quickly rose to the maximum pressure of 25 psig and the relief valve opened. I let the engine run again to make sure there wasn't any water build up. The engine started immediately and the exhaust was almost all dry steam. I then stopped the engine in a position that the inlet port to the top of the cylinder was fully open. In this position, the steam had only two places to leak. The first place was the cylinder to standard interface and it appeared almost no leakage was occurring there. The second place was by the piston packing to the exhaust side of the piston. With the engine stopped in this position the pressure wouldn't rise above 10 psig. I released the flywheel allowing the engine to run and then stopped it again in it's last position several times. Each time the engine immediately went to full speed and the exhaust was mostly dry steam. Each time I stopped the engine in this last position the pressure never rose above 10 psig. I expected the leakage would be large enough to pass all the steam the boiler was able to produce. What I didn't expect was that it could pass all the steam at such a low pressure. When I started this test, I expected it would take over 20 psig to pass all the steam. The reduction in pressure due to the leakage reduces the power significantly, but if you just want to watch the engine run without a load it doesn't matter. Also, I used the tiny pressure gage on the boiler that is very hard to get accurate pressure readings. My goal was only to get an estimate of how effective the packing is after it has been run a few hours. Based on this test, I am leaning toward O-rings for my next steam engine. I will take the cylinder apart and try to get a picture of what the packing looks like.

01/01/2019 18:31:48

Tim,

I believe the first thing you need to decide is the amount of energy you will have \available to drive the turbine. If you are scaling the size and shape of the nozzles and blades, you can make a pretty good guess of the flow required. Do you know what you plan to power your turbine with?

01/01/2019 17:39:55

Tim,

I believe the first thing you need to decide is the amount of energy you will have \available to drive the turbine. If you are scaling the size and shape of the nozzles and blades, you can make a pretty good guess of the flow required. Do you know what you plan to power your turbine with?

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